Circle inscribed in a quadrant of radius 7 cm:\nIn quadrant PQR with radius 7 cm, a circle is inscribed touching both radii and the arc. Find the exact area (in sq cm) of the circle.

Difficulty: Medium

Correct Answer: 462-308√2

Explanation:


Introduction / Context:
An inscribed circle in a quadrant (a 90° sector) is tangent to the two perpendicular radii and the circular arc. The circle’s center lies on the 45° line from the corner, giving a simple relationship between the big radius R and the small radius r.


Given Data / Assumptions:

  • Quadrant radius R = 7 cm.
  • Inscribed circle radius r satisfies distance from corner: √(r^2 + r^2) = R − r.
  • Use π = 22/7 to match the answer format without π.


Concept / Approach:
From √2 * r = R − r ⇒ r(√2 + 1) = R ⇒ r = R(√2 − 1). Then area = π r^2 = π * R^2 * ( (√2 − 1)^2 ) = π * R^2 * (3 − 2√2 ). Substitute R = 7 and π = 22/7 and simplify.


Step-by-Step Solution:

r = 7(√2 − 1).Area = π * 49 * (3 − 2√2).With π = 22/7 ⇒ Area = 49 * (22/7) * (3 − 2√2) = 154 * (3 − 2√2) = 462 − 308√2.


Verification / Alternative check:
Numeric check with √2 ≈ 1.414: r ≈ 7(0.414) ≈ 2.898; area ≈ 3.1416 * (2.898)^2 ≈ 26.4, and 462 − 308√2 ≈ 26.4, consistent.


Why Other Options Are Wrong:
Other expressions arise from incorrect placement of r or from using (R − r)^2 = r^2 instead of 2r^2.


Common Pitfalls:
Forgetting that the center-to-corner distance is along 45°, giving √2r, not r; using sector area instead of the circle’s area.


Final Answer:
462-308√2

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